An Improved Modeling of the Unsteady Flows for the Aerodynamic Noise Prediction of Coaxial Counter-Rotating Rotors

This paper presents an improved prediction model of the unsteady flows induced by the coaxial counter-rotating rotors, which will then be used as the input for noise computation. An efficient blade element momentum theory is used to compute the mean flow variables, based on which the equivalent circulations and tip vortex strength can be determined. Then, the sectional blades are unwrapped into two arrays of point vortexes on two arcs of a sector region to account for the contractive property of the wake flow. More specifically, an additional conform mapping is conducted to estimate the induced unsteady velocities due to the equivalent bound vortex, which improves a recent work by the authors {zhong2023predicting}. Moreover, the influence of the tip vortex on the induced flow and the noise radiation is included in the proposed model. Using the proposed method, we first compare the prediction results with the experimental tests in the anechoic chamber, and fairly good results are obtained. Then, the effects of separation distance and rotating speeds are studied.